Spray gun for viscous liquids



D. F. ANDERSON 2;913,187

SPRAY GUN FOR vzscous LIQUIDS 7 Filed June 20, 195'? David F ANDERS 0NUnited States Patent 2,913,187 SPRAY GUN FOR VISCOUS LIQUIDS David F.Anderson, Camden, Maine Application June 20, 1957, Serial No. 666,823 3Claims. (Cl. 239-412) The present invention relates to improvements inthe construction of spray guns and more particularly to improvements inspray guns used for viscous liquids.

While there are many and varied types of spray guns at present availablewhich function satisfactorily for the spraying of relatively thinfluids, for example, thin paints, lacquers or the like, they are not toosatisfactory when utilized for the spraying of viscous, sticky liquids,such as synthetic resins or the like.

In general these spray guns all include a liquid chamber into which thefluid is delivered under pressure and from which it is dischargedthrough a nozzle in combination with a stream of pressurized air toachieve the desired spray effect. Except where induced vacuum by thepressurized air is adequate for liquid supply, which is certainly notthe case for viscous liquids, it is necessary to provide some means ofpositively controlling and shutting off the flow of liquid at thedischarge nozzle. This is normally done by means of a needle valve whichis operated either manually or by air pressure under the control of theoperator. In some multiple spray gun arrangements for productionpurposes, the needle valves are operated in sequence by mechanicalmeans.

When seated in the discharge nozzle the needle valve retains the liquidunder pressure in the liquid chamber of the gun. To prevent the liquidunder pressure from leaking back up the valve stem and fouling theoperating mechanism, the needle valves are usually glanded or providedwith sealing washers which are forced against the stem of the valve toseal oli the valve stem accommodating boring or sleeve in the gun.Friction between these washers and/ or packing and the valve stem is aconstant source of trouble, even in the spraying of relatively thinliquids, either by retarding or completely preventing movement of theneedle valve or by permitting the liquid to leak back and clog theoperating mechanism. This is particularly true when spray guns are usedwith viscous liquids which tend to solidify in a relatively short time.

Up to the present time no really satisfactory material has been foundfrom which to make these sealing washers. Leather appears to be the bestavailable but leather absorbs the liquid being sprayed and if this isviscous or sticky, the frictional drag between washers and needle valvestem gradually increases to the point where the needle valve will notoperate.

The present invention aims to provide a solution for these problems byfurnishing a spray gun construction which is capable of handling alltypes of fluids and particularly sticky, viscous liquids such as thesynthetic resins. In accordance with the invention this is accom plishedby eliminating the need for packing washers and glands entirely withrespect to the needle valve by providing a sealed flexible diaphragm atthe rear or top of the liquid chamber. This diaphragm is constructed anddisposed within the gun body so that it not only seals off the liquid tothe interior of the chamber but also operates the needle'valve which issecured to its center.

Accordingly, the invention is a spray gun adapted for controlledspraying of viscous liquids which comprises essentially of a main bodyhaving an internal recess constituting an internal fluid chamber andhaving a sealing wall constituted by a flexible diaphragm, preferably ofmetal, extending across the internal body recess. Liquid inlet andoutlet passages are provided in the body lead ing into and out of theliquid chamber and a valve seat is provided in the outlet passage inaxial alignment with the center of the flexible diaphragm. A valve stemhaving one end shaped to conform with the outlet passage valve seat ismounted for restricted axial movement on the center of the flexiblediaphragm and in axial alignment with the liquid outlet passage. Meansare provided for adjustably restricting the amount of axial travel ofthe valve stem relative to the valve seat and consequently the degree offlexure of the flexible diaphragm under varying liquid pressuresdelivered to the fluid chamber. Means are provided to disperse the flowof liquid from the needle valve controlled outlet passage. In apreferred construction an extension is provided on the body whichincludes an atomizing air chamber having an annular discharge outletsurrounding the fluid outlet passage and there is an air inlet passageleading to the atomizing air chamber for attachment to a source of airunder pressure in the usual manner.

With this arrangement operation of the needle valve is effected bymovement of the flexible diaphragm and the diaphragm is moved by varyingthe pressure applied to the actual liquid being sprayed as it isdelivered to the liquid chamber.

Having thus generally described the nature of the invention particularreference will be made to the accompanying drawings showing a preferredembodiment by way of illustration, and in which:

Figure 1 is a side elevation of a spray gun embodying the controllingmeans of the invention;

Figure 2 is a longitudinal cross-sectional view of the construction ofFigure 1;

Figure 3 is a sectional view of Figure 2 along the line 3-3.

With particular reference to Figures 1 and 2 of the drawings a preferredconstruction of a spray gun in accordance with the present inventionincludes a main body 10 made up of interconnected portions 12 and 14.The body portion 12 is provided with a threaded end 16 and the portion14 is provided With a flanged internally threaded end 18 which fits overand is thread- =ably engaged with the lower portion end 16. A flexiblediaphragm 20, preferably of resilient metal, is mounted between the ends16, 18, of the body portions and is sealed about the outer periphery bytheir engagement to divide the interior of the gun body transversely ofits axis into chambers 24, 26.

The body portion 12 containing the liquid chamber 26 is provided withattachment extensions 28 and 30 the outer ends of which are threaded forconnection with suitable sources of fluid and pressurized air. Theextension 28 is provided with a central boring 29 constituting a liquidinlet passage leading into the liquid chamber 26 while the extension 30is provided with an offset boring 31 leading through the body portion 12to provide an air inlet passage as will be described in more detaillater.

An axial boring 32 is provided in the portion 12 and is internallythreaded to receive a correspondingly thread ed liquid discharging tipor nozzle 34. The nozzle 34 is provided with a tapering end 38 and iscentrally bored as indicated at 42, to constitute a liquid outletpassage leading from the liquid chamber 26. The outer end of the outletpassage 42 tapers due to the formation of the nozzle end 38, the innerwalls of which at this point form a tapering valve seat 44. The nozzle34 is also provided with an outstanding flange 46 provided with anannular recess 48 with which the air inlet passage 31 communicates. Aplurality of holes 50 lead from the outer surface of the nozzle flange46 into the annular recess 48 so that pressurized air delivered from theair inlet passage 31 passes into the recess 48 and through the holes 50is distributed into the interior of an atomiz ing air cap or fitting 52.

The atomizing air cap 52 is of hollow conical formationand is retainedto a threaded flanged extension 54 of the body portion 12 by a threadedlocking collar 56. The end 58 of the cap 52 is in substantial alignmentwith the terminal end ofthe nozzle'end 38- and an'air-pressure chamber60 is thus provided between the outer wall of the nozzle end 38 and theinner taperingwall of the cap 52. The spaced apart concentric ends 38and 58 of the nozzle and cap respectively provide therebetween anannular air discharge orifice 62 surrounding the liquid outlet passage42.

In order to control the discharge of liquid from the outlet passage 42,in accordance with the present invention, a valve stem 66 is mountedwithin and extends axially through the body portions 10, 12, and theflexible diaphragm 20 to which it is secured. The valve stem 66 includesa portion 68 disposed in the liquid chamber 26' and terminating in atapering end 70 adapted to seat in the liquid outlet passage valve seat44, and a portion 72 of reduced diameter disposed in the chamber 24. Thevalve stem 66 is secured to the diaphragm 20 by the abutment of ashoulder 67 at theend of the stem portion 68 on one side of the centerof the diaphragm 2i) and a retaining nut 74 threadably engaged with thestem por* tion 72. The valve stem 66 is guided for restricted axialmovement under the flexure of the diaphragm 20 by the sliding engagementof the end of the valve stem portion 72 within the boring 78 of a sleevemember 80. The sleeve member 80 is threadably engaged in a tappedopening 82 provided in the top of the body portion 12 and the valve stemreceiving bore 78 is tapped for an initial portion of its length tothreadably receive an ad justing screw 84. A coil spring 86 is mountedover the stem portion 72 and between theretaining nut 74 and the lowerend of the sleeve 80 so as to normally and resiliently urge the valvestem 66 and diaphragm 20 in a closing direction towards the liquidoutlet valve seat 44. Locking washers 88, 90, are provided on the sleeve8t) and adjusting screw 84 so as to retain these respective members inthe desired adjusted location determining the amount of axial travel ofthe valve stem 66. An attachment bracket 87 is provided on the body portion 12.

With this arrangement, operation of the valve stem 66 is effected bymovement under the flexure of the diaphragm 20. The diaphragm 20 ismoved or flexed by varying the pressure applied to the liquid deliveredto the liquid chamber 26. In use, the sleeve member 89 is adjusted toapply the desired pressure to the spring 86 and consequently thediaphragm 20. The adjusting screw 84 is then set to give the desiredstroke or move ment of the valve stem 66 (approximately A3").

Fine adjustment of the pressure control sleeve 80 and adjustment screw84 is made when spraying commences. Air pressure on the liquid supply isthen increased by opening the usual control valve (not illustrated) sothat the liquid pressure in the liquid chamber 26 overcomes the adjustedpressure of the spring 86 and moves the diaphragm 20 and valve stem 66by an amount permitted by the setting of the adjustment screw 84. Thispermits liquid to flow out of the discharge outlet passage 42.Simultaneously, in the preferred construction illustrated, air underpressure is delivered to'the air' inlet passage 31 under the control ofthe usual control valve (not illustrated). Regulation and adjustment ofthe air pressure required to operate the needle valve arrangement of theinvention is preferably eifected by a standard air pressure regulator'(not illustrated). Once set it should not be necessary for theoperatorto change the setting. The setting for the atomizing air, as is known,will'depend on the degree of atomization desired. For synthetic resinsit is an absolute minimum and here again, once set, it should needlittle further. attention. Both the air controlling the liquid pressureand the air for atomization can be conveniently controlled by asinglehandler 4 foot operated valve as is known in arrangements of thisnature.

It will be understood that nozzle arrangements other than the preferredconstruction illustrated might be utilized for the dispersing orbreaking up of the liquid stream from the outlet passage. Since theviscous type of liquid, e.g. synthetic resins, which the presentapparatus is particularly suited to handle, requires little atomizationand is preferably sprayed in fairly-large particles or droplets toachieve what is known in the art as a stippling effect, a liquid outletnozzle could be utilized which includes means to break up the liquidflow without pressurized air.

When the operator shuts oil the pressure applied to the liquid to stopspraying, a bleed valve in the liquid supply (not illustrated) willoperate in a known manner and the force of the spring 86 overcomes thepressure in the liquid chamber 26 and the valve stem 66 travels in theclosing direction seating the tapered end into seated position on theliquid outlet passage seat 44 thereby stopping the flow of liquid.

As will be understood by reference to the preceding description andaccompanying drawings the frictional retardation and other problemsencountered with the known controlling needle valves of spray guns arefor all practical purposes eliminated by the spray gun construction ofthe present invention.

I claim:

1. A spray gun construction adapted for the pressure controlled sprayingof viscous liquids comprising a main housing having an internal recessconcentric about the axis of said housing, a flexible diaphragm mountedwithin said housing partitioning said internal recess transversely ofthe axis of said housing into two chambers, said housing having at oneend an axially aligned conical extension terminating in a truncated tipand having an internal tapering recess forming a liquid dischargepassage leading from one of said housing chambers to the exterior ofsaid housing, a valve seat in said liquid discharge passage adjacentsaid housing extension truncated tip, a liquid inlet passage in the wallof said housing leading into said one chamber, a valve stem mounted insaid housing so as to extend axially through both of said chambers andincluding in said one chamber a first portion terminating in a taperedend adapted to seat in said liquid discharge passage valve seat, saidvalve stem passing through and being secured axially and concentricallyto said flexible diaphragm with the other end of said stem slidablyguided in a sleeve mounted axially withinsaid housing other chamber, aspring in said housing other chamber surrounding said valve stem andurging said flexible diaphragm and attached valve stem portionhavingsaid tapered end towards said liquid outlet passage valve seat, andmeans to disperse the flow or"- liquid from said outlet passage into aspray.

2. A spray gun construction, as claimed in claim 1, wherein said meansto disperse the flow of liquid from said liquid outlet passage comprisesa hollow pressurized gas fitting mounted on said housing conicalextension concentrically with and surrounding said extension toterminate flush with said housing extension tip and form with theexterior of said housing extension a pressurized gas chamber having aterminal annular discharge outlet.

surrounding the terminal outlet of said liquid discharge passage.

3. A spray gun construction, as claimed in claiml, wherein the saidvalve stem guiding sleeve extends exteriorly of said housing and athreaded adjustment screwis fitted in said extension sleeve portion soas to engage the end of said valve stem.

2,239,987 Bramsen et al. Apr. 29, 1941 Rabbitt .Mar. 4, 958;-

